Inductor for inductively heating a rotating workpiece

ABSTRACT

An improvement in a single shot inductor of the type used in heating the total length of an axle shaft as the shaft is rotating about its central axis. The normal single shot inductor includes two generally parallel conductors extending along the length of the shaft and terminating in cross-over conductors at each end with one of the parallel conductors including a gap for accommodating input leads connected to an alternating current source. This basic inductor is improved by providing a conductor loop including at least one auxiliary conductor extending along the outer surface of the shaft between a first position adjacent one of the cross-over conductors and a second position adjacent the other cross-over conductor, with the auxiliary conductor being magnetically coupled to the surface. The conductor loop is connected in electrical series with one of the input leads of the normal single shot inductor so that the current flow within the auxiliary conductor provides an additional heating area in the rotating shaft.

United States Patent 1 Balzer et al.

[ July 16, 1974 [75] Inventors: Norbert R. Balzer, Parma; Larry G.

Enk, Macedonia, both of'Ohio [73] Assignee: Park-Ohio Industries, Inc.

Cleveland, Ohio [22] Filed: Aug. 13, 1973 [21] Appl. No.: 388,072

52 us. Cl. 219/10.79

Primary Examiner-Bruce A. Reynolds Attorney, Agent, or Firm- Meyer,Tilberry and Body 57 ABSTRACT An improvement in a single shot inductorof the type used in heating the total length of an axle shaft as theshaft is rotating about its central axis. The normal single shotinductor includes two generally parallel conductors extending along thelength of the shaft and terminating in cross-over conductors at each endwith one of the parallel conductors including a gap for accommodatinginput leads connected to an alternating current source. This basicinductor is improved by providing a conductor loop including at leastone auxiliary conductor extending along the outer surface of the shaftbetween a first position adjacent one of the cross-over conductors and asecond position adjacent the other cross-over conductor, with theauxiliary conductor being magnetically coupled to the surface. Theconductor loop is connected in electrical series with one of the inputleads of the normal single shot inductor so that the current flow withinthe auxiliary conductor provides an additional heating area in therotating shaft.

' 11 Claims, 6 Drawing Figures PATENIED Juu 6:914

SHEET 1 BF 2 SHEET '2 [IF 2 PATENTED JUL 1 6 I974 This invention relatesto the art of induction heating and more particularly to an improvedinductor for inductively heating an elongated rotating workpiece.

The invention is particularly applicable for inductively heating aflanged axle shaft preparatory to quench hardening, and it will bedescribed with particular reference thereto; however, it must beappreciated that the invention has broader applications and may be usedin various installations wherein the standard single shot inductor isused to inductively heat the total length of an elongated, generallycylindrical'workpiece.

In hardening the outer surface of an axle shaft, it is now becomingsomewhat common practice to use a stationary inductor, known as a"singleshot-inductor. This single shot inductor includes two generally parallelconductors extending the total length of the cylindrical portion of ashaft and connected ateach end by crossover conductors generally in theform of arcuate conductors extending between the parallel conductors.One of the conductors is provided with a gap to accommodate input leadsfor directing an alternating current through a loop formed by parallelconductors and the cross-over conductors to heat inductively the shaftportion of the axle shaft as it is rotated about its central axis. Whentheaxle shaft includes a flange, one of the cross-over conductors ispositioned adjacent the'fillet area between the flange and the elongatedcylindrical shaft'portion to provide heating in the fillet area of theflanged shaft. After the rotating axle shaft has been heated to a quenchhardening temperature, the heating operation is discontinued and theshaft is quench hardened. This procedure for inductively heating thesurface of an axle shaft has been quite successful; however, certaindifficulties have been experienced. To provide sufficient heating in arelatively short period of time high power densities are necessary. Asthe power is switched on and off, the inductor flexes primarily at thejoint between the parallel conductors and the crossover conductors. Thisrepeated flexing can cause fatigue cracks in the inductor. Since theinductor includes internal coolant passages, in accordancewith normalpractice, these fatigue cracks cause leakage of the coolant and requirereplacement of the inductor when they develop. Many attempts have beenmade to prevent the premature failure of single shot inductors. Forinstance, reinforcing ofthe inductor has been used. This does increasethe life of the inductor; however, such reinforcing is relativelyexpensive and requires substantial man hours to accomplish. Otherattempts have included reducing power density of the inductor. Thisincreases the heating time which is not satisfactory because it adds tothe cost of the heating operation.

The present invention is directed toward an improved single shotinductor which increases the life and efficiency of the inductor.

In accordancewith the present invention, the standard single shotinductor is modified to include a conductor loop including at least oneauxiliary conductor extending along the shaft surface of the axle shaftand between a first position adjacent one cross-over conductor and asecond position adjacent the other crossover conductor. The auxiliaryconductor is magneti cally coupled to the shaft surface and there areprovided means for connecting the conductor loop in elec- By using thepresent invention, a reduced current can.

be directed through the inductor and still develop the necessary heatingof the workpiece surfaces in a relatively short time.

In accordance with another aspect of the present invention, theauxiliary conductor is adjacent one of the parallel conductors and thereis means for causing the current flow in the auxiliary conductor to bein phase with the current flow in the adjacent parallel conductor. Inthis manner, the two conductors create fields whichare additive in theirheating effect.

The primary object of the present invention is the provision of animproved single shot inductor of the type defined above, which inductorincludes a separate conductor loop having at least one conductoradjacent the surface thereof to increase the heating effect by theinductor and thus reduce the required flux densities of the inductor.

Yet another object of the present invention is the provision of animproved single shot inductor of the type defined above, which inductorrequires a reduced flux density and, thus, increases the life of theinductor.

Yet another object of thepresent invention is the provision of animproved single shot inductor of the type defined above, which inductorhas a longer life during operation and a higher heating efficiency thanprior single shot inductors for the same workpiece.

These and other objects and advantages will become apparent from thefollowing description taken together with the accompanying drawings inwhich:

FIG. I is a pictorial view illustrating the preferred embodiment of thepresent invention;

FIG. 2 is a top elevational view of the preferred embodiment shown inFIG. 1;

FIG. 3 is a side elevational view, partially in crosssection, showingthe preferred embodiment of the present invention as illustrated in FIG.1;

FIG. 4 is an enlarged cross-sectional view taken generally along line4-4 of FIG. 3;

FIG. 5 is an enlarged cross-sectional view taken generally along line5-5 of FIG. 3; and,

FIG. 6 is an enlarged cross-ectional view taken generally along line 6-6of FIG. 3.

Referring now to the drawings wherein the showings are for the purposeof illustrating the preferred embodiments' of the invention only, andnot for the purpose of limiting same, FIGS. l3 show an induction heatinginstallation A for inductively heating the outer generallycylindricalsurface of an elongated workpiece, such as axle shaft B, byan inductor C. The workpiece includes a cylindrical body portion 10having an outer cylindrical surface, a flange 12 connected onto the bodyportion 10 by a fillet 14. In accordance with normal practice,.there isprovided means for rotating the workpiece B about its central axis a.Various arrangements can be used for rotating the workpiece; however, inaccordance with the illustrated embodiment of the'invention, a rotatingmotor 20 rotates the workpiece as it is supported between normal centers22, 24.

The inductor C includes two generally parallel conductors 30, 32extending substantially the total length of body portion 10 andterminating in axially spaced cross-over conductors 34, 36 which aregenerally concentric with the surface of portion 10 and spaced there- 31+ 7 from in accordance with the induction heating practice. Theinductor C is considered to be a single inductor; however, as is wellknown in the induction heating art, this inductor includes a gap 40 todefine spaced input leads 42, 44. Of course, the input gap can beprovided in'any of the conductors 30, 32, 34, and 36. As so farexplained, inductorC does not differ from the normal single shotinductor used for inductively heating axle shafts preparatory to quenchhardening. The cross-over conductor 34 is adjacent fillet 14 for thepurpose of heating the fillet portion and a part of the flange forsubsequent quench hardening.

In accordance with the present invention, there is provided anadditional heating structure for inductor C. This structure includes aconductor loop 50 connected in electrical series with the input lead 44of the previously described portion of the'inductor. Conductor loop 50includes a parallel conductor 52 positioned adjacent parallel conductor32 and best shown in FIGS. 4-6. The parallel conductor 52 forms anauxiliary conductor forproviding additional heating to surface asworkpiece-B is rotated by motor 20. The improved inductor includes anadditional parallel conductor 54 formed in conductor loop 50. As was thecase with conductor 30, conductor 54 is considered to be a singleconductor spaced from and adjacent to conductor-30; however, theconductor 54, for electrical purposes includes two separate portionsdivided by a central gap 56 similar to gap 40 of conductor 30. Tocomplete the electrical circuit of loop 50, there are provided crossoverconductors 60, 62 generally concentric with axis a. Conductor 60 isadjacent cross-over conductor 36, and conductor 62 is adjacentcross-over conductor 34. As best seen in ,FIG. 1, conductor 60 'is anarcuately shaped conductor spaced axially from conductor 36 and spacedfrom the cylindrical surface of portion 10 substantially the samedistance as the cross-over conductor 36. In the flange area of workpieceB, the crossover conductor 62 is radially spaced from conductor 34 andterminates in lower connecting portions 64, 66 which connect thearcuately shaped cross-over conductor 62 with the lower parallelauxiliary conductors 54, 52, respectively. By using these connectingportions, the auxiliary conductors 52, 54 can be positioned in magneticcoupling relationship with cylindrical portion 10 and below theconductors 30, 32, respectively. In this manner, four elongated parallelconductors are in heating relationship with the body portion 10 as theworkpiece is rotated. i

To provide alternating current for energizing inductor C, auxiliaryconductor 54 at the position adjacent input lead 44 is provided with aninput lead 68 connected with the auxiliary conductor 54 by a connectingportion 70 which allows the input lead 68't0 be positioned generally inthe same plane as the input lead 42 of parallel conductor 30. A sourceof alternating current, schematically represented as generator 80includes output leads 82, 84 connected onto leads 42,68 to createalternating current flow through the inductor C. By providing thearrangement as illustrated in the figures, the current flow withinconductors 30, 54, conductors 32, 52, conductors 34, 62, and conductors,36, 60 are in phase. This phase relationship is indicated by the arrowsin FIG. 1. In view of this arrangement, the

flux fields created by the primary and auxiliary conductors in all areasof inductors C are additive and do not cancel each other during theinduction heating operation. It is appreciated that the flux densityabout each conductor within inductor C can be reduced and still createheating effect equivalent to the heating caused by increased fluxdensity in prior single shot inductors. This is accomplished because ofthe increased length of the current path in the inductor. A reduced fluxdensity creates a lesser flexing action during cycling of the inductor.In addition, there are increased number of connections betweencross-over and parallel conductors to absorb the flexing action. Forthese reasons, the life of the inductor is increased by reducing thepropensity to create fatigue failure of the inductor. The reduced fluxdensity causes a lesser outward force on the inductor during the heatingoperation. As a larger area is affected during the heating operation,the efficiency of the heating operation can also be increased. I

In accordance with normal practice, L-shaped high permeability fluxconcentrating elements are provided on cross-over conductors 34, 62 asshown in FIG. 3. In a similar manner, U-shaped flux concentrators 92 canbe provided over the cross-over conductors 36, 60. These fluxconcentrators can be provided along the length of the parallelconductors to increase the heating efficiency of the total installation.The use of these high permeability flux concentrators is well known inthe art and does not form a part of the present invention.

Having thus described our invention, we claim:

1. An improvement in an inductor for inductively heating an elongatedcylindrical workpiece having an elongated body portion with a generallycylindrical outer surface as said workpiece is being rotated about acentral axis, said inductor including a pair of elongated generallyparallelconductors extending along.

said cylindrical surface and generally parallel to said axis; a firstcross-over conductor joining said parallel conductors at one of theirends; a second cross-over conductor joining said parallel conductors atthe opposite ends thereof; and, input means for passing an alternatingcurrent through said conductors as said workpiece is rotating, saidinput means including two input leads connected ata gap in one of saidparallel conductors, the improvement comprising: said input meansfurther comprising a conductor loop including at least one auxiliaryconductor extending along said surface and between a first positionadjacent said first crossoverconductor and a second position adjacentsaid second cross-over conductor, said auxiliary conductor beingmagnetically coupledto said surface and means for connecting saidconductor loop in electrical series with one of said input leads.

2. The improvement as defined in claim 1 wherein ,said auxiliaryconductor-is generally parallel to said parallel conductors and adjacentone of said parallel conductors.

3. The improvement as defined in claim 2 including means for causing thecurrent flow in said auxiliary conductor to be in phase with the currentflow in said one parallel conductor.

4. The improvement as defined in claim 3 wherein said conductor loopincludes a secondauxiliary conductor generally parallel to and adjacentto the other of said parallel conductors.

5. The improvement as defined in claim 4 wherein said conductor loopincludes a cross-over conductor extending between said auxiliaryconductors and generally concentric with said cylindrical outer surface.

6. The improvement as defined in claim 5 wherein said cross-overconductor of said conductor loop is adjacent to said first cross-overconductor and including means for causing the current flow in saidcross-over conductor of said connector loop to be in phase with thecurrent flow in said first cross-over conductor.

7. The improvement as defined in claim 6 wherein said cross-overconductor of said conductor loop is spaced axially from said firstconductor and spaced from said outer surface a distance generally equalto the spacing of said first cross-over conductor from said surface.

8. The improvement as defined in claim 6 wherein said cross-overconductor of said conductor loop is spaced radially from said firstcross-over conductor and generally concentric with said first cross-overconductor.

9. The improvement as defined in claim 1 wherein said conductor loopincludes an arcuate conductor extending circumferentially with respectto said outer surface and magnetically coupled to said surface.

10. The improvement as defined in claim 9 wherein said arcuate conductoris adjacent said first cross-over conductor and including means forcausing the current flow in said arcuate conductor to be in phase withthe current flow in said first cross-over conductor.

11. The improvement as defined in claim 10 wherein said arcuateconductor is spaced axially from said first cross-over conductor andspaced from said outer surface a distance generally equal tothe spacingof said first cross-over conductor from said surface.

1. An improvement in an inductor for inductively heating an elongatedcylindrical workpiece having an elongated body portion with a generallycylindrical outer surface as said workpiece is being rotated about acentral axis, said inductor including a pair of elongated generallyparallel conductors extending along said cylindrical surface andgenerally parallel to said axis; a first cross-over conductor joiningsaid parallel conductors at one of their ends; a second cross-overconductor joining said parallel conductors at the opposite ends thereof;and, input means for passing an alternating current through saidconductors as said workpiece is rotating, said input means including twoinput leads connected at a gap in one of said parallel conductors, theimprovement comprising: said input means further comprising a conductorloop including at least one auxiliary conductor extending along saidsurface and between a first position adjacent said first cross-overconductor and a second position adjacent said second cross-overconductor, said auxiliary conductor being magnetically coupled to saidsurface and means for connecting said conductor loop in electricalseries with one of said input leads.
 2. The improvement as defined inclaim 1 wherein said auxiliary conductor is generally parallel to saidparallel conductors and adjacent one of said parallel conductors.
 3. Theimprovement as defined in claim 2 including means for causing thecurrent flow in said auxiliary conductor to be in phase with the currentflow in said one parallel conductor.
 4. The improvement as defined inclaim 3 wherein said conductor loop includes a second auxiliaryconductor generally parallel to and adjacent to the other of saidparallel conductors.
 5. The improvement as defined in claim 4 whereinsaid conductor loop includes a cross-over conductor extending betweensaid auxiliary conductors and generally concentric with said cylindricalouter surface.
 6. The improvement as defined in claim 5 wherein saidcross-over conductor of said conductor loop is adjacent to said firstcross-over conductor and including means for causing the current flow insaid cross-over conductor of said connector loop to be in phase with thecurrent flow in said first cross-over conductor.
 7. The improvement asdefined in claim 6 wherein said cross-over conductor of said conductorloop is spaced axially from said first conductor and spaced from saidouter surface a distance generally equal to the spacing of said firstCross-over conductor from said surface.
 8. The improvement as defined inclaim 6 wherein said cross-over conductor of said conductor loop isspaced radially from said first cross-over conductor and generallyconcentric with said first cross-over conductor.
 9. The improvement asdefined in claim 1 wherein said conductor loop includes an arcuateconductor extending circumferentially with respect to said outer surfaceand magnetically coupled to said surface.
 10. The improvement as definedin claim 9 wherein said arcuate conductor is adjacent said firstcross-over conductor and including means for causing the current flow insaid arcuate conductor to be in phase with the current flow in saidfirst cross-over conductor.
 11. The improvement as defined in claim 10wherein said arcuate conductor is spaced axially from said firstcross-over conductor and spaced from said outer surface a distancegenerally equal to the spacing of said first cross-over conductor fromsaid surface.